1. Field of the Invention
The present invention relates to a method of and apparatus for manufacturing a semiconductor device and, more particularly, to a method of and apparatus for manufacturing a ball bump formed on an electrode pad of a semiconductor chip.
2. Description of the Prior Art
Conventionally, in a semiconductor device such as a film carrier semiconductor device and a flip-chip, bumps as metal projections are formed on the electrode pads of a semiconductor chip (to be referred to as an IC chip hereinafter). Generally, a metal bump made of Au or a solder is selectively formed on an electrode pad by electroplating through a barrier metal layer constituted by a diffusion preventive layer or a adhesive layer. Several methods have conventionally been proposed to replace electroplating bump formation.
An example of such a substitutional proposal is a ball bump method disclosed in Japanese Patent Application Laid-Open Document No. Sho 49-52973. According to this method, a ball is made from a wire made of Au, a solder, or the like by wire bonding, the ball is bonded on an electrode pad, and the wire is cut to leave only the ball, thus forming a bump. This ball bump method is generally practiced by using an automated ball bump bonding apparatus.
A conventional ball bump bonding apparatus has a semiconductor wafer loader 10, a wafer setter (to be referred to as a wafer stage 11 hereinafter), a wafer storage 12, a ball bump bonding head 13, a recognition camera 14, a recognition unit 15, a wire feeder 16, manipulators 24 for moving the bonding head 13 in the X and Y directions, and an operation panel 25, as shown in the outer appearance of FIG. 1. The function of the conventional ball bump bonding apparatus will be described.
As shown in FIG. 1, a wafer on which IC chips are formed is conveyed from the wafer loader 10 to the wafer stage 11, positioned on a bonding stage by urging its orientation flat against pawls or the like, and fixed on the wafer stage 11 by vacuum chucking. Then, the wafer is imaged by the recognition camera 14, the positions of the IC chips on the wafer are detected by the recognition unit 15, the electrodes pads on the IC chips are ball-bonded on the basis of the prestored coordinates data in accordance with the ball bump bonding technique described above, and the wires are cut to attach ball bumps to non-defective IC chips. When ball bumps are formed on all the non-defective IC chips on the wafer, the wafer is conveyed to the wafer storage 12.
Conventionally, if the ball bump bonding apparatus is stopped due to an error, e.g., wire disconnection while automatic ball bump bonding is performed using this apparatus, the wire-disconnected state shown in FIG. 2A wherein the distal end of a wire 17 is retracted in a capillary 18 must be restored to a state shown in FIG. 2B wherein a ball 22 is formed at the distal end of the wire 17, thereby restoring the automated operation. For this purpose, the following procedures are taken. The wire 17 is passed through the capillary 18, as shown in FIG. 3A, the manipulators are manually operated, a defective IC chip which is detected in advance is searched for on a monitor screen, and the bonding head 13 and a bonding arm 20 are moved above the defective IC chip. Then, the wire 17 is urged against the electrode pad on the defective IC chip on a wafer 23 by the capillary 18, as shown in FIG. 3B, a wire clamp is closed while moving the capillary 18 upward, and the wire 17 is cut at its portion urged between the wafer 23 and the capillary 18. A torch rod 21 performs electric discharge toward the wire 17, as shown in FIG. 3C, to form a ball 22 at the distal end of the wire 17, as shown in FIG. 3D.
With this conventional ball bump bonding apparatus, when the apparatus is stopped due to an error, e.g., wire disconnection, a defective IC chip on the wafer must be found in order to set the wire in the ball-up state, that is, in order to form a ball at the distal end of the wire. It is time-consuming to find the defective IC chip. If no defective IC chip is found on the wafer, non-defective IC chips are wasted.